Photonic crystal enhanced-fluorescence and label-free bioimaging

Photonic crystal surfaces supporting guided-mode resonances are used for label-free and enhanced fluorescence bioimaging. First, theory is developed and supporting simulations are used to optimize photonic crystal devices for both label-free sensing and enhanced fluorescence. A model is presented for predicting label-free biosensor performance based on the spatial distribution of electromagnetic near-fields at device resonance. A comparison of device sensitivity calculated by both the model and direct rigorous coupled wave analysis simulation supports the validity of the theory. An improved understanding of resonant near-fields supported by photonic crystals is then applied to enhance the output of fluorophores residing near the device surface. Simulation data support a methodology for maximizing the overlap of high-intensity near-fields with surface-bound fluorophores.;The results of these two studies are applied to the optimization and fabrication of a single photonic crystal designed to support both biosensing techniques. A new imaging instrument employing expanded laser illumination is developed to optimally interface with this structure, and is shown to be capable of generating registered label-free and enhanced fluorescence images with 328x more sensitive fluorescence detection relative to a glass surface. The two imaging techniques are applied to a DNA microarray where label-free quantification of immobilized capture DNA facilitates improved quality control and subsequent enhanced fluorescence detection of dye-tagged hybridized DNA enables 3x more genes to be detected versus commercially available microarray substrates.;In further work, a theory is outlined for predicting photonic crystal label-free imaging resolution based on resonance spectral characteristics. Devices are characterized by patterning a resolution standard onto the sensor using photolithography, and excellent design control over label-free imaging resolution is demonstrated. The spectral response of a photonic crystal is optimized for improved label-free imaging of immobilized DNA microarray capture spots. Applications to protein microarrays and cell-based assays are also demonstrated.